Incandescent electric lamp



Patented Apr. 12, 1927.

UNHTED STATES PATENT OFFICE.

WILLIAM CHARLES SPBOESSEB, OF BLOOMFIE'LD, fi'EW JERSEY, ASSIGNOB r0WES!- IBIGHOUSE LAMP COMPANY, A COBPOBA'IION.OF PENNSYLVANIA.-

INOAN'DESCENT ELECTBIO LAMP.

Ho Drawing.

M invention relates to electrical devices em l bying incandesciblemetallic filaments, an more particularly it relates to electricincandescent lamps.

In the manufacture of incandescent lamps employing filaments of arefractory material, such as tungsten and the like, it is customary, inone stage of the process through which these lamps are carried in thecourse of their fabrication, to pass an electrical current through thefilament. This operation, known in the art as flashing, is alwayspracticed after the lamp has been exhausted and permanently sealed-01f,and

- one of its objects is to vaporize a material, which is commonly termeda getter and which has been placed within the lamp, preferably on thefilament. The function of the getter substance is well known to thoseversed in the art and various theories have been advanced by skilledartisans concerning its action in assisting the lamp in properlyfunctioning. It may be stated, however, with reference to the getter,that its principal uses are confined to the elimination of the darkdeposit of filamentary material upon the inner walls of the envelope,which affects the candle-power maintenance value of the lamp, and alsothat it serves to overcome the harmful effects of the residual gasesremaining within the lamp after exhausting and which are due to poorexhaust or to occluded gases which come off at some period subsequent tothat operation.

The theories which have been offered in explanation of the getteraction, as well as the literature relating to such substances, do notmention utilizing the getter in a manner which will improve the strengthof the filamentary structure, after flashing, over that which itnormally would have if the customary flashing schedules were followedand well-known getter materials were employed.

That it is very desirable to increase the present strength of the lampfilaments after flashing is evident when it is considered that ashrinkage occurs in the factory and during shipment of about five-tenthsof one percent of the total output. This shrinkage has been directlytraced to the weakened condition of the filaments resulting fromimproper crystal growth during flashing.

Application filed December 8, 1921. Serial No. 518,784.

In order to avert such losses, I have sought to improve the strength ofthe lamp filament to such an extent that the usual shocks which a lampmay be subjected to in transit w1ll be msuflicient to cause itsbreakage. It s, therefore, an ob'ect of my invention to improve thestrengt of filaments over that which is normally obtained when presentmethods are practiced.

Many lamp failures also occur during the course of manufacturing thelamp, particu larly during the flashing operation, which may beattributed to arcs which form across the leading-in wires and filamentsections. These arcs frequently melt down the leading-in wires ,andfilaments and thus render the lamp worthless. It is believed that theformation of these arcs may be induced by the ionization of the residualgases within the envelope resulting from poor exhaust; or else may beaided by the favorable medium afforded the current by the vaporizinggetter material; or it may even be that the combination of these actionsmay be the cause, or that other reasons may prevail. Sometimes thiselectrical action occurs while the lamp is being burned or duringseasoning thereof, but regardless of whatever may be the cause of thiselectrical phenonmenon or when it may occur, it is one of the objects ofmy invention to substantially prevent such injurious action.

Certain other lamp failures during flashing and seasoning are known asburnouts, which result from a filament burning out in one or more spotsthroughout its length, thus shortening its life. My invention is alsodesigned to eliminate this detrimental feature.

Still another defect is the collection of the getter material in beadshere'and there along the filament which results in the formation of hotand cold spots throughout the length of the filament. This condition isproductive of improper crystal growth during the recrystallizationstage, and since a uniform grain structure produces the strongestfilament it is obvious that the irregular formation of the crystalscaused by beading greatly weakens the filament. The improved gettermaterial which I employ includes a constitutent which prevents thegetter material from beading in the manner indicated above.

.With the present forms of getters it appears almostimpossible toprevent occasional lamps from slumping, thatis, suddenly decreasin incandle power during the life of the Iamps. The reason why such actionoccurs is not very well understood.

It is, however, very desirable to prevent the lamps from performing inthis manner since the users may very readily consider the cause thereofas either carelessness in manufacture or poor quality of materials. Theimproved getter which I have devised prevents lamps from performing inthe manner just mentioned.

It is the purpose of my invention, in view of the foregoing factors, toprovide a process for treating metallic filaments, such as areordinarily employed in lamps, whereby the crystalline formation may becontrolled when the lamp is initially lighted, so that a structure or anarrangement of crystals may be obtained which will be productive of afilament having a strength considerably greater than that which can beobtained under present practice.

An additional object of my invention is to provide a getter materialwhich, when employed in practicing my process, will be productive of anelectric incandescent lamp of the vacuum and other types having asomewhat increased candle power maintenance, a more consistentperformance throughout its life and a filament of increased strength. Inother words, the lamp produced according to my process and practicedwith the getter discovered by me is more 'efiicient in so far asfilament strength is concerned than any commercial lamp heretoforeproduced.

These objects, as well as other objects, will be apparent from a readingof the following description.

My invention may be briefly stated as comprising a process whichconsists in controlling within certain limits by means of gettersubstances, the temperature to which the selected filamentary materialis raised upon initial lighting whereby a crystalline growth is producedduring the recrystallization stage which is productive of the maximumstrength filament after the same has been thus lighted. The gettermaterials which I find preferable to employ in order to effect thecontrol desired, includes those having high melting point substances, asI have determined with such substances present in the etter a moreefiicient product may be obtained. Up to thepresent time the mostsatisfactory results are obtainable when the melting point of thematerial added to the getter is approximately equal to the germinativetemperature of the selected filamentary material under conditions of afirstclass vacuum. The reason for this will be more fully appreciatedhereinafter.

By getter substances, I mean such sub- 4 drawn structure does notremain, but instead a change or recrystallization occurs during whichaction the original elongated crystals break-u tion. t is also observedthat when these new crystals are of uniform dimensions and of small sizeand are distributed regularly throughout the length of the filament thatthe latter is much stronger than when the crystalline formation isirregular, that is, in groups of large crystals intermingled with groupsof smaller fine-grained crystals, or even when the crystals aredistributed regularly but are relatively large in size. Further,metallurgical investigations have led to the discovery that wherefilaments are raised to high temperatures the crystalline growthisexcessive.

In practicing present processes for flashing the getter substance in thelamps, proviinto a smaller crystalline formasion has been made byplacing resistance in series with the filament to prevent the currentpassing through the filament from reaching proportions sufficientlylarge to detrimentally heat the same. In spite of the precautions taken,however, the filaments become heated to temperatures which aredetrimental to the desired crystal growth. I have discovered that thetemperatures to which the filaments are raised during the flashingtreatment may be governed by employing substances which will consume aportion of the heat energy which passes through the filament whenflashed, so there will be no likelihood of the filament becomingexcessively heated. In order to secure the desired action it ispreferable to placethe substances in thermal conductive relationship tothe filament. My experiments have demonstrated that a substance orcompound having a high melting point is preferable to those of lowervolatilization temperatures although I have proven that the latter alsoproduces increased filament strength upon flashing. It is preferablethat the high-melting poin material possesses the property of beingsubstantially inactive with respect to the filamentary material. Bysubstantially inactive I mean that any compounds which may be formed bythe combination of such substance and the filamentv or residual gases,must be of such nature that they do not produce detrimental effects uponthe life, quality or candle power maintenance of the lamp. It ispreferable to employ only such compounds or substances which are whollyinactive. However, in view of the high which exist in electemperatureconditions articularly those of trio incandescent lam s,

the vacuum type, an t e high vacuum unpossible to determine whether ornot the particular substances, hereinafter more fully identified, areinactive or not.

In practice it is preferable to add the high melting point substance toany of the well-known getter materials and aflix the mixture in anydesired manner to the lamp filament.

It is my belief that the action of the substance added to the getterserves to control the temperature to which the filament may be elevatedand that it holds this temperature within certain bounds and at leastprevents the temperature from rising to such a degree that detrimentalcrystal growths progress. Why the added material should operate in themanner indicated is not well understood, but it is possible the actionmay be that during the transition of the added substance from the liquidor solid state .into the vapor condition, the re uisite amount of heator energy required to e ect such change, that is, the latent-heat ofvaporization, is obtained by absorption or otherwise from the filament,thus efiecting a reduction in the amount of energy or heat within thefilament. It will thus be seen that the compound protects the filamentsfrom high temperatures. Although the above explanation is advanced insupport of the action of the added substance it is to be understood thatother equally plausible theories may be advanced; therefore, I do notwish to be understood as limiting this invention by any particularexplanation made herein.

During the flashing of lamps which have been treated with a high-meltingpoint substance of the character indicated, it is observed that thecustomary blueing or areing which occurs when ordinary getters areemployed does not result. The reason why the presence of thehigh-melting point substance, which prevents the occurrence of thisphenomena, which latter, as explained above, is frequently injurious tothe lamps, is not well understood. It is possible, however, that becauseof the presence on the filament of the highly refractory compound, ionicemission is suppressed. Furthermore, it is probable that a sufiicientquantity of the refractory compound remains on the filament to protectit from the bombardment of positive ions, which, some believe, resultsin the pitting and, therefore, the weakening of the filament. By reasonof the highlyrefractory compound preventing arcing it has been foundfeasible to burn lamps treated with such a compound directly on acommercial circuit without previously having been subjected to aflashing treatment, thus indicatmg the practicability of eliminatingthat step in the fabrication of electric incandescent 1am s. Theaddition of the high-melting point substance to the getter prevents thegetter from accumulating in beads along the filament at initial li htinthus permitting a uniform distribution 0 that ingredient of the (omoundwhich prevents blackening of the lnner walls of the envelo Havingdescribed the iifoader aspects of my'invention, I shall now cite aspecific application thereof. My preferred process is to first prepare agetter mixture. containing the following active ingredients inapproximately the following percentages by weight: silicon oxide 40%cryolite 50% and phosphorus 10%. A homogeneous mixture may be made ofthese substances and a thin coating thereof may be applied in anydesired manner to the filamentary material. The coating maybe dried andthereafter the coated filament severed into appropriate lengths andmounted in an mcandescent electric lamp envelope in the usual manner.The envelopes may be evacuated and permanently sealed-off. If agas-filled lamp is being manufactured, the nitrogen, argon or other gasshould first be introduced into 9 the envelope prior to sealing-off.

The lamps thus formed may then be subjected to an initial burning orheating, commonly called flashing, which operation heretofore had asingle purpose, namely that of flashing off the getter, but which, withmy improved getter, has the additional function of flashing-off theadded substance which operates to regulate the temperature to which thefilament is raised during the flashing steps. The flashing operation maybe conducted in accordance with the present schedules and atapproximately the designed voltages and the usual percentages ofcurrent. During the flashing operation the phosphorus constituent of thegetter being of low vaporization temperature will be the first of thematerials to vaporize, and in its vaporized state it combines with theresidual gases to elimlnate their detrimental effects 1 and to assist informing a first-class vacuum. The cryolite is next vaporized andfunctions as the candle power maintenance ingredient. The material ofhigh vaporization temperature, in this case the silicon oxide, is nexvaporized and because of the time required-- to complete itstransformation to a vapor. state due to its high latent heat ofvaporization, the phosphorus and cryolite constituents are enabled tofully complete their respective functions. The high vaporizationingredient also prevents the cryolite and phosphorus from beading alongthe filament with the result that the filament is heated up uniformlythroughout its entire length,

thus serving to reduce to a minimum the malformation of crystal growths.

Through tests made under operating conditions I have demonstrated thatlamps treated with getters having silicon oxide therein burn atincreased cfliciencies during the full length of their lives. Inaddition, I have observed that the length of the life of a lamp may beshortened without affecting its operating efliciency by addingpredetermined amounts of silica.

An example of another getter mixture wherein the silicon oxide issubstituted by another compound, is one having its active ingredients inthe proportions by weight as follows: aluminum oxide 30%, cryolite andphosphorus 10%. Getters which in clude in regulated amounts othermaterials of high vaporization temperatures as mentioned above, havebeen successfully employed, as, for instance, beryllia 15%, cryolite7.5% and phosphorus 10% Although I have enumerated refractory oxides asthe added or heat controlling ingredient, it should be understood, thatthe use of all refractory compounds which do not detrimentally reactwith the filamentary material are contemplated by my invention.

N OW that I have described my process and the ingredients of the getter,which will be found particularly advantageous in practicing the same, itis to be understood that such modifi'ations as suggest themselves and.

which fall within the scope of the appended claims are rontemplated bymy invention.

What is claimed is:

1. The process of controlling the crystal growth in a metal lampfilament when initially heated which consists in coating said filamentwith a compound having a high volatilization temperature and which willnot react detrimentally with said filament or the residual gases withinthe lamp.

2. The process of controlling the crystal growth in a metal filament ofan electric incandescent lamp during flashing which consists inintroducing into said lamp on the filament thereof a refractorysubstance capable of volatilization at the flashing temperature.

3. The process of treating the metal filament of an electricincandescent lamp to effect an increased strength on the filament afterflashing, which consists in uniformly distributing over said filament achemical compound capable of promoting a uniform temperature conditionthroughout the length of said filament.

4. The process of controlling the crystal growth in metal filamentsduring flashing, which consists in preventing the temperature of saidfilament from substantially exceeding the germinative temperaturethereof by applying a heatabsorbing medium as a coating to saidfilament.

5. In an electric incandescent lamp an incandescible metal body having achemical coating thereon of a high vaporization temperatureapproximating the germinative temperature of said body.

6. In an electric incandescent lamp an incandescible metallic filamenthaving a refractory oxide getter applied directly to the surfacethereof.

7. In an electric incandescent lamp an incandescible metallic filamentcoated with a refractory oxide, said oxide being incapable of combiningwith said filament.

8. In an electric incandescent lamp a metal filament having a coating ofsilicon oxide.

9. In an electric incandescent lamp a metal filament having a getterapplied thereto, said getter having a refractory compound as one of itsconstituent substances.

10. In an electric incandescent lamp a metal filament having a gettercomposed of cryolite, phosphorus and an inert refractory substance.

11. In an electric incandescent lamp a metal filament having a gettercomposed of cryolite, phosphorus and a substantially inert compoundhaving a high volatilization temperature.

.12. In an electric incandescent lamp a metallic filament having agetter composed of cryolite, phosphorus and silicon oxide.

13. A getter directly applied on an incandescible filament andcontaining a substantially inert refractory substance.

14. A getter directly applied upon a refractory metal filamentandcontaining silicon oxide.

15. A. getter comprising cryolite, phosphorus and a substantially inertrefractory oxide.

' 16. A getter comprising cryolite, phosphorus and silicon oxide.

In testimony whereof, I have hereunto subscribed my name this 2 day ofDecember, 1921.

WILLIAM CHARLES SPROESSER.

